Field of the Invention
The present invention relates to a system for the preparation of beverages by brewing, using prepackaged capsules, preferably of the sealed type, containing a quantity of a substance, for example ground roast coffee, for the preparation of a beverage.
Background
More specifically, the invention relates to a system comprising, in a known way:                capsules of at least a first type and a second type, having respective outwardly protruding transverse flanges, and respective different axial lengths, and        a brewing unit, in which there is defined a variable-volume brewing chamber with a lateral delimiting part and a slidable end delimiting part, for receiving capsules of said first and second type introduced into said chamber.        
A system of this type for the preparation of beverages is described and illustrated in European patent application EP 1 208 782 A1.
In this known system, a capsule, selectively of a first or a second type, is made to bear on a loading plate which, by means of a manually operated control lever, is then translated horizontally and subsequently raised vertically, so as to introduce this capsule into the brewing chamber formed in a percolation unit. The arrangement is such that the operation of the control lever simultaneously causes a lowering of the percolation unit. The latter comprises a lateral delimiting part of the brewing chamber, in which an end delimiting part of said chamber is vertically slidable in a liquid-tight way. Because of the coupling between the loading plate and the percolation unit, the capsule causes a movement of the delimiting part of the brewing chamber, as a function of the axial length of the capsule. The percolation unit is also provided with a device for locking the end delimiting part of the brewing chamber. This locking device comprises a transverse locking pin which can be pushed so as to engage with said end delimiting part of the brewing chamber by a cam member, in the terminal part of the operating stroke of the aforesaid control lever.
In this known system, the capsules must have a rather robust structure, since it is their bodies that act by means of mechanical force to cause the volume of the brewing chamber to be adapted to the axial length of the capsule used.
International patent application WO2004/112556A1 describes another system comprising a machine including a brewing unit with a variable-volume chamber into which the user can selectively introduce one or more capsules of filter paper.